Four years ago, Martin Roesch started work in his Eldersburg, Md., living room on a program to ward off such damaging attacks on fragile technology systems. What started as a weekend hobby for Roesch, a techie with expertise in network security, . . .
Four years ago, Martin Roesch started work in his Eldersburg, Md., living room on a program to ward off such damaging attacks on fragile technology systems. What started as a weekend hobby for Roesch, a techie with expertise in network security, soon turned into aserious business opportunity. "I became very aware that the Internet was big and not going to be getting any smaller any time soon," said Roesch, 32, who has done contract work for National Security Agency. "There's a lot of opportunities to do some good things."

He wrote a program called Snort, a network intrusion detection system that sniffs out suspicious activity, such as intrusive hackers. The product was "open source," or free for anyone to download and use. In its first year of operation, there were 10 million downloads from the program's Web site, according to SecurityFocus Online, a Web site that studies the industry.